The instant invention relates to a method of treating cellulose di-acetate fibers to reduce the shrinkage characteristics thereof.
Cellulose di-acetate fibers and garments made therefrom normally exhibit excessive shrinkage characteristics, particularly when they are subjected to laundering and steam pressing. In this connection, fabrics made of untreated cellulose di-acetate fibers frequently shrink as much as six to seven percent when subjected to steam pressing and as much as eight to nine percent when subjected to laundering. To further complicate matters shrinkage of cellulose di-acetate fibers is generally non-uniform and hence can result in distortion of fabrics and garments made therefrom.
Several processes have heretofore been available for the treatment of cellulosic fibers to achieve improved shrinkage control. Resination of cellulosic fibers using thermosetting resins has proven to be an effective method of controlling shrinkage of viscose cellulosic fibers but has proven to be impractical for controlling shrinkage of cellulose di-acetate fibers. This results from the fact that when thermosetting resins are applied to cellulosic fibers they crystallize when catalized and they also cause crosslinkage between the fibers. Both of these phenomena have weakening effects on cellulosic fibers. Acid catalysts which are used to catalize such resins also tend to have weakening effects on cellulosic fibers. While some of these weakening effects can be tolerated when treating viscose fibers which are naturally relatively strong fibers, they cannot be tolerated when treating cellulose di-acetate fibers which are inherently weak fibers. Further, weakening effects are realized when treating cellulose di-acetate fibers as opposed to other types of cellulose fibers as a result of the fact that the curing temperatures which are necessary in resination methods are normally detrimental to cellulose di-acetate fibers. Because of all of these factors, it has been found that when cellulose di-acetate fibers are treated for shrinkage control using conventional resination techniques they are weakened to the point that they can no longer be effectively used in fabrics or yarns. Hence, the conventional techniques utilized for shrinkage control of other types of cellulosic fibers have been found to be inapplicable to the treatment of cellulose di-acetate fibers. For similar reasons, other conventional fabric treatment techniques, such as those used to effect improved water repellency and/or stain resistance, have proven to be impractical for the treatment of cellulose di-acetate fibers, particularly because of the excessive curing temperatures required by such methods.
The instant invention relates to a method of treating cellulose di-acetate fibers to reduce the shrinkage characteristics thereof without adversely effecting fiber strength. In accordance with the method of the instant invention the cellulose di-acetate fibers are first immersed in a treating solution comprising an organic resin, a nonionic fluorocarbon long chain polymer, an acid liberating catalyst and a carrier which preferably comprises water plus a water soluble organic solvent. The fluorocarbon polymer plus the resin comprise between 2 and 25 weight percent of the treating solution, the ratio by weight of polymer to resin is between one-to-one and four-to-one and the solvent is an organic solvent of the type which can be volatilized at a temperature below 300.degree. F. and of the type which can be mixed with the fluorocarbon and the resin without reacting therewith. The fibers with a quantity of the solution thereon are then removed from the solution and dried at a temperature below 300.degree. F., to drive off substantially all of the water and solvent therefrom leaving only the resin, the fluorocarbon polymer and the catalyst on the fibers. In the final step of the method the fibers with the resin-fluorocarbon-catalyst mixture thereon are cured at a temperature in excess of 300.degree. F. to polymerize the resin and effect cross-linkage thereof with the fluorocarbon polymer. It has been found that cellulose di-acetate fibers treated in this manner exhibit substantially improved shrinkage characteristics without being significantly weakened. Further, cellulose di-acetate fibers treated in this manner exhibit memory characteristics which provide advantages in the use thereof in fabrics.
While solutions comprising water, water soluble organic solvents, organic resins, nonionic fluorocarbon long chain polymers and acid liberating catalysts have heretofore been used in the treatment of other types of synthetic fibers, they have been used primarily to improve the water and oil repellency of such fibers and they have not provided improved shrinkage characteristics. Further, such solutions have had relatively high polymer to resin ratios in order to avoid significant fiber stiffening. Due to the fiber weakening effects which have been realized when cellulose di-acetate fibers have been treated by conventional methods, such solutions have normally been considered to be impractical for use on cellulose di-acetate fibers.
Because of the ineffectiveness of virtually all of the heretofore known shrinkage control and water repellency treatments for cellulose di-acetate fibers, heretofore the concensus has been that the effective treatment of cellulose di-acetate fibers with solutions containing significant quantities of organic resins and/or fluorocarbon polymers was impossible. The method of the instant invention departs from this concensus to achieve effective shrinkage control of cellulose di-acetate fibers through the nonobvious application of a solution comprising a fluorocarbon polymer plus a relatively high concentration of a thermosetting resin. The curing techniques utilized in the method of the instant invention also depart substantially from what would normally be considered to be proper for cellulose di-acetate fibers. Specifically, curing is effected at temperatures in excess of 300.degree. F. which would normally be considered to be detrimental to such fibers. In fact, 300.degree. F. is well above the recommended maximum safe ironing temperature for cellulose di-acetate fibers (the ASTM standard for maximum safe temperatures for cellulose di-acetate fibers is 250.degree. F. to 275.degree. F.). While curing temperatures in excess of 300.degree. F. have been used in the treatment of other types of fibers, they have not been used on cellulose di-acetate fibers for this reason, therefore, it has been unexpectedly found that by the use of what would normally be considered an inappropriate treating solution for cellulose di-acetate fibers, and the use of what would normally be considered as excessive curing temperatures, unexpectedly achieve highly beneficial effects in cellulose di-acetate fibers.
It is, therefore, the primary object of the instant invention to provide an effective method of treating cellulose di-acetate fibers to improve the shrinkage characteristics thereof.
Another object of the instant invention is to provide a process of improving the shrinkage characteristics of cellulose di-acetate fibers without causing weakening of the fibers.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds as hereinafter set forth.